A polyaminoamide is one of curing agents for epoxy resins and "polyaminoamide" is a general term for compounds which contain a plurality of active amino groups and at least one amide bond per molecule (according to "International Organization for Standardization"). A polyaminoamide is chiefly obtained by condensation between a polymeric fatty acid such as a dimeric acid or a trimeric acid and a polyamine compound such as polyethylene-polyamine. Since the polymeric fatty acid is a mixture comprising from 70 to 80% by weight of a dimer, from 15 to 25% by weight of a trimer and a tetramer, and not more than 10% by weight of a monomeric fatty acid, a variety of polyaminoamides are produced with variations of the kind or amount or the polyamine compound to be reacted with the polymeric fatty acid. Thus, the structural composition of polyaminoamides cannot be expressed in a simple manner.
The above-mentioned polyaminoamides are mainly employed as a cord-cure (i.e. at room temperature) type curing agent for epoxy resins. However, compared with polyamine compounds also used as an epoxy resin curing agent, the polyaminoamide is less reactive, with the number of amino groups being equal, because of the increased molecular weight due to the condensed polymeric fatty acid. As a result, it takes longer time for the former to achieve complete curing.
Where it is demanded to cure an epoxy resin at a higher rate or in a lower temperature, a polythiol compound is often employed as a curing agent. However, in order that a polythiol compound may exhibit rapid curing properties or cold curing properties, a basic compound must be used in combination as a curing accelerator. Additionally, most of the currently employed polythiol compounds are polythioalkylcarboxylates obtained by the reaction between a thioalkylcarboxylic acid and a polyhydric alcohol, and the presence of an ester bond in the resulting molecule makes such polythiol compounds inferior in chemical resistance, particularly alkali resistance. Therefore, epoxy resins cured by the use of the polythioalkylcarboxylates are not allowed to be used in applications involving contact with an alkali.
Further, the polythioalkylcarboxylates form hydrogen sulfide gas on epoxy resin curing reaction, resulting in not only deterioration of the working environment but entrapment of gas bubbles and corrosion. Use of them has therefore been limited.